Toothbrushes generally include bristle tufts made of a plurality of bristle filaments mounted onto the head of an oral brush handle. During the manufacturing of the brush heads, the bristles for said bristle tufts are cut from longer bristle filament strands into the required length. Thereby, sharp and irregular edges are generated at the bristle ends which might cut or irritate the oral surfaces, in particular the gums and the gum lines. Depending on the manufacturing technique both ends of a bristle become working ends (i.e.—the ends that contacts the teeth and gums) or only one end of the bristle will contact the oral surfaces after being mounted into the final brush head. That means at least the working ends of the bristles have to be smoothened in order to remove the sharp edges produced during cutting into working length. This smoothening process is known as end-rounding.
End-rounding of the bristle filaments can be performed at different time points during the manufacturing proceedings. In anchor tufted brush heads, the bristles are pre-cut, folded into two and then clamped into a blind-hole at the brush head using a metal wire. After all bristle tufts have been mounted onto the brush head by anchor tufting, the final tuft profile is cut and the bristle ends of the whole tuft pattern are end-rounded (U.S. Pat. Nos. 3,416,262 A1, 2,227,126 A1, 3,619,953 A1, 2,554,777 A1). If anchor-free mounting techniques are used, one of the bristle ends is mounted into the brush head or a part thereof and only the opposite bristle end is used as working end. Usually, in these manufacturing procedures the bristles are cut and end-rounded at the working end before they are mounted into the brush head or the part thereof, e.g. using an end-rounding device as disclosed in DE 10 2004 054 839 A1.
Nowadays complexity of bristle tuft pattern and surface profile with respect to the whole brush as well as with respect to the individual bristle tufts continuously increases. In addition, very smooth and sensitive toothbrushes are needed for people with hyposensitive gums and gum lines. Thus, smoothening, in particular end-rounding of bristles have to meet high quality standards.
In most end-rounding methods, the working ends of the bristles are contacted with an abrasive material, such as a sanding disc, which is rotated using an electric motor. For example an abrasively coated and convex formed disc which is mounted for rotation about a central axis is used in commonly known end-rounding apparatus (U.S. Pat. No. 3,451,173). Later on said convex formed disc were amended into triangular shaped disc, wherein the end-rounding was performed with one of the flat, but angled, surfaces (U.S. Pat. No. 5,165,761). Alternatively, rotating cylinders having an abrasive surface can be used (WO 1999/07255 A1). The drive systems for the rotating abrasives may be commonly known electric motors or higher sophisticated driving systems, such as an air driven planetary gear system (WO 2002/94059 A1).
During the end-rounding proceedings not only the individual bristles have to be smoothened sufficiently, but also the quality of end-rounding should not deviate significantly over the complete tuft or tuft pattern. The more bristle filaments are end-rounded in one process step, the more discrepancies arise regarding the end-rounding result of the individual bristle. In particular this problem exists, if higher numbers of bristles filaments, such as provided by filament hanks or hanklets, are end-round in parallel. Thus, a continuous need exists to improve end-rounding equipment and end-rounding methods, in particular with respect to end-rounding equipment or end-rounding methods which can be used for higher numbers of bristle filaments.